With the use of any form of electrical equipment that includes high voltage or high current carrying conductors, there is typically a need for heat dissipation qualities of the insulating materials. With the push to continuously reduce the size and to streamline all electrical and electronic systems, there is a corresponding need to find better and more compact insulators and insulation systems.
Various organic polymer thermoset resin materials, like epoxy, polyester, and phenolic formulations, have been used extensively in electrical insulation systems because of the practical benefits they possess; they are tough and flexible electrical insulation materials that can be easily adhered to surfaces. Traditional high voltage electrical insulation materials, such as mica particles in flake or splittings form and glass fiber, can be surface coated and bonded with common thermoset polymeric resins to produce composite materials with increased mechanical strength, chemical resistance, and electrical insulating properties. In many cases, epoxy based polymeric resins are used due to their adjustable liquid properties, excellent bond strength to variety of materials and outstanding dielectric properties.
Good electrical insulators, by their very nature, also tend to be good thermal insulators; a property which is undesirable. Thermal insulating behavior, particularly for air-cooled electrical equipment and components, reduces the efficiency and durability of the components, as well as the equipment as a whole. It is desirable to produce electrical insulation systems that have maximum electrical insulation and minimal thermal insulation characteristics.
Electrical insulation often appears in the form of insulating tapes, which themselves have various layers. Common to these types of tapes is a dielectric layer that is bonded at an interface to a carrier layer for tensile strength, both layers tending to be impregnated with a polymeric resin. A favored type of electrical insulation material is mica-tape. Improvements to mica-tapes include catalyzed mica-tapes as taught in U.S. Pat. No. 6,103,882. The mica-tape may be wound around conductors to provide extremely good electrical insulation. An example of this is shown in FIG. 1. Illustrated here is a coil 13, comprising a plurality of turns of conductors 14, which in the example illustrated here are assembled into a bakelized coil. The conductor insulation 15 is prepared from a fibrous material, for example, glass fabric or glass mat and Dacron mat, or polymeric films made from polyester or polyimide which is heat treated. Ground insulation for the coil is provided by wrapping one or more layers of composite mica tape 16 about the bakelized coil 14. Such composite tape may be a paper or felt of small mica flakes combined with a pliable backing sheet 18 of, for example, glass fiber cloth or polyethylene glycol terephthalate mat, the layer of mica 20 being bonded thereto by a liquid resinous binder. Generally, a plurality of layers of the composite tape 16 are wrapped about the coil depending upon voltage requirements. A wrapping of an outer tape 21 of a tough fibrous material, for example, glass based tape, may be applied to the coil.
Generally, multiple thin layers of the mica tape 16 are wrapped about the coil with sixteen or more layers usually being used for high voltage coils. Polymeric resins are then impregnated into the tape layers. These impregnating resins can also be used as insulation independently from the insulating tape. Unfortunately, this amount of insulation further adds to the complications of dissipating heat. What is needed is electrical insulation that can conduct heat with higher conductivity than that of conventional methods, without compromising the electrical insulation and other performance factors, including mechanical and thermal capability, as well as being able to be used in a wide range of applications.
Other difficulties with the prior art exist, some of which will be apparent upon further reading.